(a) Field
The subject matter disclosed generally relates to solid sources and methods for the synthesis of gaseous precursors used in the Chemical Vapor Deposition (i.e., CVD). More particularly, the subject matter disclosed relates to solid sources for the synthesis of gaseous silicon-containing precursors used in the CVD of silicon-based ceramic thin films used for, without limitation, protective coatings, refractory ceramics, and thin films for electronic and semiconductor devices.
(b) Related Prior Art
Chemical vapor deposition (i.e., or CVD) is a chemical process used to produce high-purity and/or high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD processes, the wafer (i.e., the substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through a reaction chamber.
Microfabrication processes widely use CVD to deposit materials in various forms, which include, without limitation, monocrystalline, polycrystalline, amorphous, epitaxial and the like. These materials include, without limitation, silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, various high-k dielectrics and the like.
For example, U.S. Pat. No. 7,396,563 to Scarlete et al. discloses a semiconductor thin film of amorphous silicon carbide obtained through vapor deposition following desublimation of pyrolysis products of polymeric precursors in inert or active atmosphere. This Polymer-Assisted Chemical Vapor Deposition (PA-CVD) allowed one or multi-layers compositions, microstructures and thicknesses to be deposited on a wide variety of substrates.
European Patent no. EP 2,122007 to Awad et al. discloses a method for forming a film on a substrate. The method comprises the steps of heating a solid organosilane source in a heating chamber to form a gaseous precursor, transferring the gaseous precursor to a deposition chamber, and reacting the gaseous precursor using an energy source to form the film on the substrate. The film comprises Si and C, and optionally the film comprises other elements such as N, O, F, B, P, or any suitable combination. However, according to this method, CVD of the film changes. However, the a) higher average temperature and b) high thermal gradient in the section of the solid source, induced by the conductive heating of the solid organosilane source used in this method, both required for the formation of the gaseous precursors (inhomogeneous distribution in the section of the solid source resulting in a much higher temperature on the outer shell that in the core of the solid source) produces a high amount of low molecular weight, volatile carbosilane species with negative impact on the yield of the transformation of the solid source into the desired gaseous precursor—dimethylsilane.
US Patent Publication no. 2010/0051096 to Kim, D. S. et al. discloses a silicon solar cell which comprises an antireflective coating, which coating comprises amorphous silicon carbonitride, and where the amount of carbon in the silicon carbonitride is from 5 to 25 atomic %. The gaseous mono-silicon organosilanes are obtained from pyrolysis of a solid organosilane source, such as polydimethylsilane. This document shows that C-containing silicon-based ceramic films can be used for the fabrication of solar cells.
US Patent Publication no. 2010/0186811 to Kim, D. S. et al. discloses an antireflective coating for silicon-based solar cells which comprises amorphous silicon carbonitride, a solar cell comprising the antireflective coating, and a method of preparing the antireflective coating from one or more gaseous mono-silicon organosilane obtained from pyrolysis of a solid organosilane source, listing polydimethylsilane, polycarbomethylsilane, triphenylsilane, or nonamethyltrisilazane for example. This document shows that C-containing silicon-based ceramic films can be used for the fabrication of solar cells.
National Institute of Standards and Technology (NIST) in “Layered graphene sheets could solve hydrogen storage issue” (2010, Mar. 19), and J. Burress, J. Simmons, J. Ford and T. Yildirim in “Gas adsorption properties of graphene-oxide-frameworks and nanoporous benzene-boronic acid polymers” (American Physical Society Meeting, Mar. 18, 20101, Portland, Oreg.) reported that grapheme-oxide frameworks (GOF) can accumulate hydrogen in large quantities. The description of hydrogen-supports like the one described here does not come with the possibility of eliminating the hydrogen-deficit of PDMS with respect to improved stoichiometrical (i.e., full) decomposition in DMS. Rafiee J. et al. from Renssselar Polytechnic Institute have reported a novel form of engineered graphene that exhibits hydrogen storing capacity far exceeding any other known material. No connection is mentioned with respect to a possible usage of this material for obtaining improved decomposition of PDMS into DMS.
Yang Yang and Richard Kaner, from the California NanoSystems Institute (CNSI), have reported a technology for making graphene sheets in big quantities and at a low price. No connection is mentioned in this method with respect to a possible usage of this material for obtaining improved decomposition of PDMS into DMS.
Morgan, D. et al. presented in their CRS' Report for Congress 95-540 SPR the capability of hydrogen storage and controlled release via glass microspheres. These are small, hollow, glass micro-balloons which have diameters that vary from about 25 microns to 500 microns (i.e., 1/1000 inch to 20/1000 inch), and which have wall thicknesses that are about 1 micron. They can be used in large beds to store hydrogen at high pressures. The microspheres are filled with hydrogen gas at temperatures of 200 to 400 degrees Centigrade. The high temperature makes the glass walls permeable, and the gas fills the spheres. Once the glass is cooled to room temperature, the hydrogen is trapped inside the spheres. This document allows exact control of the temperature of H-delivery in the system. The composition of the glass could be arranged such that at the Tg, a high amount of H is abruptly delivered in the system. However, this document allows for efficiency only if the H-storage property of graphite is lower than the practical required level for the stoichiometric decomposition of PDMS into DMS. No connection is mentioned in this method with respect to a possible usage of this material for obtaining improved decomposition of PDMS into DMS.
The generation of gaseous precursors from the source is currently based on conductive and radiative heating. Processing of a 250 g charge of solid source requires a continuous 5-15 kW supply from an electrical resistor over 4-8 hours. There is therefore a need for an improved solution for the transfer of the energy required by this reaction.
Bulk graphite is commonly used as susceptor for radio frequency heating (i.e., RF heating). For example, Berkman et al. discloses in U.S. Pat. No. 3,980,854 a susceptor for heating a plurality of semiconductor wafers, by RF induction, comprising a hollow truncated pyramid of conventional graphite.
In another environment, Kaeppeler et al. discloses in U.S. Pat. No. 7,048,802 the use of graphite foam for depositing crystalline layers on crystalline substrates by means of reaction gases fed to a heated process chamber. This process chamber is formed by the cavity of an especially multi-part graphite tube arranged in a reactor housing that especially comprises quartz walls. This reactor housing, in the area of the process chamber, is enclosed by a high-frequency coil and the space between the reactor housing and the graphite tube is filled with a graphite foam sleeve.
Additionally, synthesis of graphite flakes which includes grapheme layers is disclosed in U.S. Pat. No. 7,754,184. In this patent, a process for the production of nano-structures is presented, involving the steps of providing a graphite flake comprising graphene layers, intercalating the graphite flake to form a graphite intercalation compound exhibiting Stage I, II or III intercalation, and exfoliating the graphite intercalation compound under conditions such that a plurality of individual graphene layers are separated from the graphite intercalation compound.
Silicon carbide can also be used as susceptor material. Koag et al. discloses in U.S. Pat. No. 5,119,540 a method, and associated apparatus and product, for forming extremely pure epitaxial layers of silicon carbide by reducing the carrier concentration of residual nitrogen in silicon carbide formed by chemical vapor deposition processes. The method comprises placing a substrate upon which an epitaxial layer of silicon carbide will form upon a susceptor. U.S. Pat. No. 5,119,540 takes advantage of the fact that, although the breaking of Si—Si bonds which is the onset for Kumada rearrangement starts as low as 200° C., the quantitative production of this rearrangement which is carbosilane is observed only around 400° C.
There is therefore a need for improved solid sources and methods for the synthesis of silicon-containing precursors for chemical vapor deposition and/or for the synthesis of gaseous precursors used in the chemical vapor deposition of silicon-based ceramic thin films used for, without limitation, protective coatings, refractory ceramics, and thin films for electronic and semiconductor devices.